A Case of Maternal Half-sisters Sharing Alleles at 18 X-chromosomal Short Tandem Repeat Loci

Abstract

Analysis of X-chromosome short tandem repeats (STRs) is very helpful in deficiency paternity testing. Here, we reported a case of kinship analysis that showed a potentially erroneous inclusion of paternal sisters between two women. The two women shared alleles at 18 X-chromosomal STR loci spanned from 14.76cM (DXS6807) to 184.19cM (DXS7423). When their relatives were not available for testing, biostatistical analysis for the 18 X-chromosomal STR loci and 24 autosomal STR loci revealed the most possible relationship between the two women was paternal sisters. However, when the father of one woman was available, the other father-daughter possibility was excluded. In the end, the likelihood ratio of STR marker and mitochondrial DNA (mtDNA) sequences confirmed the two women were maternal sisters. This case emphasizes a cautionary interpretation of X chromosomal marker in deficiency paternity cases with female offspring. Even though large parts of the X-chromosome haplotypes shared by two females, additional relatives and extended DNA typing (such as mtDNA) may be needed further to ascertain whether they are paternal or maternal sisters.

Keywords

• Haplotype
• kinship testing
• recombination
• X-chromosome short tandem repeat